二维阵列分配问题

这是我朋友昨天被问到的一个面试问题。问题是:这个程序是否会因“访问冲突”错误而崩溃?我看了一会儿,觉得不行,不行。但事实证明,在Visual Studio中进行这种尝试是错误的。我不知道这里发生了什么…或者更准确地说,我知道发生了什么,但不明白为什么。问题似乎是Matrix2数组根本没有被分配。

代码如下:

#include <iostream>
#include <ctime>

using namespace std;

int** matrixAlloc( const int rows, const int cols );
void matrixAlloc( int** matrix, const int rows, const int cols );
void matrixDealloc( int** m, const int rows);
void matrixPrint( const int* const * const m, const int rows, const int cols );

int main( int argc, char** argv )
{   
    srand( (unsigned int)time( NULL ) );
    int** matrix1 = matrixAlloc( 4, 5 );
    matrixPrint( matrix1, 4, 5 );
    matrixDealloc( matrix1, 4 );

    int ** matrix2 = NULL;
    matrixAlloc( matrix2, 4, 5 );
    matrixDealloc( matrix2, 4 ); // <--- crash occurs here  
}

int** matrixAlloc( const int rows, const int cols )
{
    int **matrix = new int *[ rows ];
    for ( int i = 0; i < rows; i++ )
    {
        matrix[ i ] = new int[ cols ];
        for ( int j = 0; j < cols; j++ )
        {
            matrix[ i ][ j ] = (rand() * 12347) % 10;
        }
    }

    return matrix;
}

void matrixAlloc( int** matrix, const int rows, const int cols )
{
    matrix = new int *[ rows ];
    for ( int i = 0; i < rows; i++ )
    {
        matrix[ i ] = new int[ cols ];
        for ( int j = 0; j < cols; j++ )
        {
            matrix[ i ][ j ] = (rand() * 12347) % 10;
        }

    }
}

void matrixDealloc( int** matrix, const int rows )
{       
    for ( int i = 0; i < rows; i++ )
    {
        delete [] matrix[ i ];
    }
    delete [] matrix;
}

void matrixPrint( const int* const * const matrix, const int rows, const int cols )
{
    for ( int i = 0; i < rows; i++ )
    {
        for ( int j = 0; j < cols; j++ )
        {
            cout << matrix[ i ][ j ] << " ";
        }
        cout << endl;
    }
    cout << endl;
}